Glare-directed imaging

ABSTRACT

Imaging that uses glare to confirm proper measurement of a sample. An imaging device illuminates an object and generates glare (i.e., specular reflection, diffuse reflection or a combination of the two) off the object&#39;s surface, which is displayed on a display as a glare artifact. The location of the glare artifact is compared to a predetermined location to establish adjustment to obtain a desired angular orientation. The imaging device optionally highlights the glare artifact and steers a user to obtain the desired presentation angle. In two other embodiments, the spatial relationship between the imaging device and the object is time-varied. In one, the imaging device monitors changing glare and acquires a measurement when a desired glare is detected. In the other, the imaging device captures multiple images including varying glare artifacts and analyzes the images to select a preferred image having a glare artifact indicative of a desired angular orientation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.10/146,752, filed May 16, 2002 now U.S. Pat. No. 7,006,210, and claimsthe benefit of U.S. Provisional Patent Application No. 60/291,446, filedMay 16, 2001 and entitled GLARE POSITIONING TECHNIQUES FOR IMAGING OFSAMPLES WITH REFLECTANCE MEASURING INSTRUMENTATION.

BACKGROUND

The present invention relates to measuring characteristics of an objectsuch as color, translucence, contrast, texture, roughness and the like.More particularly, the invention relates to optically measuring thesecharacteristics for an object that generates glare when illuminated.

When an object having a smooth, glossy surface is illuminated withlight, some of that light usually is reflected in a way that degradesviewing of the object, for example, by creating a bright white spot thatappears to be emanating from the object. This bright spot is associatedwith an optical phenomena referred to as “glare.”

Glare is generated by beams of light from an illumination source beingreflected from an object's surface directly along an observation line ofan observer, or an optical device, such as an imaging device or acamera. In most cases, glare is a reflected image of the light sourceitself. FIG. 1 illustrates the interaction of a light beam generated byillumination source 3 with a surface 10 to generate glare, i.e.,reflected light beam 8, as viewed by observer O. Incident light beam 2,refracted light beam 4 and reflected light beam 8 interact with surface10 under Snell's law, which provides that the angle A of incident lightbeam 2 is equal to the angle B of reflected light beam 8 as referencedto an axis 5 normal to the surface. Refracted light beam 4 interactswith the object. Portions of beam 4, when redirected by interaction toemerge from the object, may be observed by observer O along observationlines 6 to provide useful information, such as color, transparency,texture, etc., about the object. However, where the observer'sobservation lines 6 coincide with the reflected light beam 8, theobserver can only perceive a bright spot appearing to emanate from thesurface at point C. This bright spot is referred to as a glare artifact.

Although not a significant problem in casual human observation, glareprovides many challenges in photographic and imaging applicationsbecause it detracts from captured images and eliminates usefulinformation, e.g., color, contrast, translucency, etc., in locationscoinciding with glare artifacts in the images. Accordingly, manyconventional imaging devices are configured to manage reflected lightbeams, particularly light beams reflected from glossy or shiny surfaces,and prevent them from reaching the imaging device to generate glareartifacts in images.

A typical glare-eliminating imaging instrument, shown in FIG. 2,includes a directional light source 3 and an imaging device 12. Thesecomponents are geometrically positioned to prevent the reflected lightbeams 8 from reflecting along an observation axis 14 of the imagingdevice 12, which is at a 45 degree angle from normal to the glossysurface 10. Specifically, the illumination source 3 is configured toproject light beams 2 toward the glossy surface 10 along lines normal tothe surface. Under Snell's law, the incident light beams 2 generatereflected light beams 8, which reflect toward the light source at anangle normal to the surface. Accordingly, the reflected light beams arenot coincident with observation axis 14 nor observation lines 6, andtherefore are not detected by the imaging device 12. Thus, no glare isseen by the instrument or generated in resulting images.

Another glare-reducing imaging instrument design uses polarized light toreduce glare artifacts. Specifically, an illumination source projectslight polarized at one angle and an imaging device includes a filter totransmit light to the device at a different angle. Reflected light iscross-polarized out from any resulting image.

Although most conventional imaging processes attempt to reduce theimpact of glare in captured images, a few actually use it, but only forlimited purposes. For example, U.S. Pat. No. 6,222,628 to Corallomeasures the intensity of glare from a sample to determine the roughnessof a metal surface. In U.S. Pat. No. 5,764,874 to White, the intensityof glare is measured in regions of cigarette paper coated with glue andcompared to the measured intensity of glare in regions not coated withglue to ensure that enough glue is applied to the paper. In anotherexample, a specific type of glare-specular reflection from a glossysurface-is used to reconstruct a three-dimensional shape of an objectfrom a two-dimensional image of the object. Specifically, thethree-dimensional surface shape of an object is calculated by analyzinglocations of specular reflection in either multiple images from multipleviewpoints under one light, or multiple images from a single viewpointunder a different light sources. H. Shultz, Shape Information fromMultiple Images of a Specular Surface, IEEE Transactions on PatternAnalysis and Machine Intelligence, 16:195-201 (1994).

Until recently, conventional imaging devices have been designed toreduce the effect of glare on image capture. And even now, the intensityof glare is used only in specific applications to analyze attributes ofglare-generating surfaces or extract three-dimensional information fromtwo-dimensional images. Thus, many opportunities exist to exploit theinformation provided by glare.

SUMMARY OF THE INVENTION

The present invention is directed to a process of exploiting glareinformation to obtain a desired measurement of an object. Moreparticularly, the invention uses glare information to assist a user inobtaining a desired orientation of an imaging device relative to anobject to be measured.

In a preferred embodiment of the invention, glare information is reliedon to adjust the angular orientation of an imaging device and an objectmeasured relative to one another. More specifically, to satisfactorilymeasure a reflectance characteristic such as color, translucency,contrast, and related appearance variables including texture and gloss,a desired angular orientation, is acquired by positioning a glareartifact in a predefined location in an image of the object. To do so,the object is illuminated with a glare-generating light source. Theimage, including measured glare artifacts created by theillumination—typically indicated as bright white spots—is displayed on adisplay. By positioning the glare artifacts in a “predefined” or “ideal”location in the image, the imaging device is substantially reorienteduntil the desired angular orientation of the imaging device and objectrelative to one another is attained.

In a more preferred embodiment, the imaging device outlines orhighlights measured glare artifacts and/or the ideal location of theglare artifacts on the display. Thus, a user can identify the measuredglare artifacts and/or the ideal location of the artifacts to adjust theangular orientation of the imaging device until the measured artifactsregister with the ideal locations in the image.

In an even more preferred embodiment, the imaging device “steers” theuser, or an associated image device holding mechanism, to adjust theimaging device to the desired angular orientation. The imaging deviceanalyzes an image of an object to determine the measured locations ofglare artifacts in the image. These measured locations are compared toideal locations of the glare artifacts. If the comparison indicates thatthe measured and ideal locations do not coincide, then the imagingdevice computes a steering function corresponding to the change in theangular orientation necessary to relocate the measured location near orcoincident with the ideal location. The steering function preferably isdisplayed on the display to steer the user in repositioning the imagingdevice. Where the imaging device is supported on a holding mechanism,the steering function is used to control the mechanism and adjust theimaging device.

In a second embodiment, the imaging device monitors the changing glareinformation of a passing object to determine when the object is in adesired orientation for acquiring an image including a satisfactorymeasurement of reflectance characteristics. For example, in a conveyanceline, an imaging device determines the orientation of an object as itsrelationship to the imaging device changes based on the position ofglare artifacts associated with the object. When the imaging devicedetermines that the glare artifact is in a location that is indicativeof a desired angular orientation, the imaging device captures an imageof the object.

In a third embodiment, the imaging device captures multiple images of apassing object. A user or the imaging device selects those images withglare information positioned in preferred regions of the image thatcoincide with desired illumination or a desired angular orientation ofthe imaging device and object relative to one another. Measurements maybe taken from regions of interest in the selected images with confidencethat the illumination or angular orientation was satisfactory.

In a fourth embodiment, an imaging device is provided that includesmultiple, glare-generating illumination sources. When an object isilluminated with these sources, and imaged by the imaging device, theresulting image includes multiple measured glare artifacts. Byreconciling the measured glare artifacts with corresponding ideal glareartifact locations, it is possible to determine with increasedconfidence that the imaging device and measured object were in a desiredangular orientation when the image was acquired.

In a fifth embodiment, the imaging device includes one or moretime-varying illumination sources that produce multiple, different glareartifacts in images captured by the imaging device. By reconciling thesemany glare artifacts with corresponding ideal glare artifact locations,it is possible to ensure the desired angular orientation is achievedduring measurement.

The present invention offers many benefits. First, the invention usesglare information to assist a user in obtaining a desired angularorientation of an imaging device relative to a measured object. This, inturn ensures that a captured measurement or image contains useful data.Second, the imaging device of the invention can identify glare artifactsin an image for a user to assist the user in adjusting the device. Thisis useful when imaging glossy objects, and even more useful when imagingmatte-finish objects, which typically do not generate well-defined glareartifacts. Third, with time-varied positioning of imaged objects, glareinformation is effectively used to determine when an object is properlyilluminated or the device is properly oriented to subsequently acquireuseful measurements or images of the object. Fourth, when multipleimages of a moving object are captured, glare information may be used toselect useful measurements or images. Fifth, with multiple illuminationsources or time-varied illumination sources, it is possible to generatemore glare artifacts which may be reconciled with corresponding, idealglare artifact locations to confirm with a high degree of confidencethat desired angular orientation is achieved.

These and other objects, advantages and features of the invention willbe more readily understood and appreciated by reference to the detaileddescription of the invention and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of observation of specular reflectionin the prior art;

FIG. 2 is a side elevational view of a specular reflection-eliminatingimaging device of the prior art;

FIG. 3 is a side elevational view of the imaging device of the presentinvention measuring a sample;

FIG. 3A is a detail view of an illuminated sample including a diffusespecular reflection;

FIG. 4 is a perspective view of the imaging device measuring anddisplaying a sample;

FIG. 5 is a side elevational view of the imaging device in apre-measurement orientation;

FIG. 6 is a perspective view of the imaging device in thepre-measurement orientation;

FIG. 7 is a perspective view of the imaging device in a measuringorientation;

FIG. 8 is a side elevational view of the imaging device held in afixture to study glare and an angular orientation;

FIG. 8A is a display of a commercially available shade tab reference;

FIG. 9 is a side elevational view and output view of first and secondalternative embodiments of the present invention;

FIG. 10 shows a perspective view of a third alternative embodiment ofthe imaging device of the present invention including multipleillumination sources; and

FIG. 11 shows a perspective view of a fourth alternative embodiment ofthe imaging device of the present invention including a time varyingillumination source.

DETAILED DESCRIPTION OF THE INVENTION I. Overview

An imaging device constructed in accordance with a preferred embodimentof the invention as illustrated in the drawings and generally designated20. Major components of the imaging device are illustrated in FIG. 3 andinclude an illumination source 40, an image sensor 50, a processor 60and a display 70. Although the imaging device is depicted as a portableinstrument, it may also be stationary with the independent componentsmounted in relation to a sample as desired.

The illumination source 40 illuminates a sample 22 and the image sensor50 captures images through the viewing port 21. The image sensor 50 isin communication with the display 70, and the display displays capturedinformation as an image. Both the display 70 and the image sensor 50 maybe in further communication with a processor 60 that analyzes theinformation captured by the image sensor 50 and displayed on the display70.

In use as shown in FIGS. 3 and 4, a sample 22 is placed adjacent theviewing port 21. Light from illumination source 40, that is, incidentrays 180-183, passes out the viewing port 21 to impinge on the sample22. Many rays are reflected from the surface of the sample 22, includingreflected specular rays 184, 185 and 188. Some of the specular reflectedrays, for example, 188 and 185, are directed back along the optical axis52 of the image sensor 50. Other rays, for example diffuse reflected ray186, also are directed toward the image sensor 50 for capture and lateruse in reflectance measurement (described below). Other reflected rays,such as reflected specular ray 184, are reflected away from the imagesensor. The image sensor captures an image of the sample 22 in theperspective perceived by the image sensor, including the reflected rays188, 185 and 186 and a region of interest 28. In the areas from whichreflected specular rays 188 and 185, are reflected toward the imagesensor, glare artifacts 24 and 26 are generated. These artifacts arealso captured by the sensor.

Where the sample 22 also includes a matte-finish surface, for example inregion 189 shown in FIG. 3A, the rays reflected from the sample mayfurther include diffuse specular ray 187, which may or may not bereflected toward and captured by the image sensor 50.

The image sensor transfers information to the display 70, which displaysan image 23 of the sample. The image includes image glare artifacts 25and 27 corresponding to glare artifacts 24 and 26 of the sample fromwhich rays 180 and 185 are reflected. The image produced on the display70 can be viewed to determine whether the imaging device 20 is properlyoriented relative to the sample, preferably so that the optical axis 52of the image sensor is normal to the surface of the sample in the regionof interest 28.

Predefined locations 30 and 32, either known to the user or provided onthe display 70, are used to guide orientation of the imaging device.Specifically, when the glare artifacts 25 and 27 are substantiallycoincident with the regions 30 and 32, respectively, the user canconfirm that the imaging device is in the desired angular orientation.

With the desired angular orientation of the imaging device 20 relativeto the region of interest 28 established, a user may be confident thatthe region is properly captured in image 23. Accordingly, that regionand the reflectance characteristics of the sample 22 in the region 28 orother regions, if desired, may be analyzed. “Reflectancecharacteristics” refers to any of the following, alone or incombination: color, translucence, contrast, and related appearancevariables including relative gloss value, texture and roughness.

Reference in this application is made to the terms “specularreflection,” “diffuse reflection,” “diffuse specular reflection,”“glare” and “glare artifact.” As used herein, “diffuse reflection”refers to light that has penetrated into an object, is scattered withinit and emerges, in part at an angle that is captured by a image sensor,camera, or observed by a viewer. “Specular reflection” means light thathas only interacted with the surface of the object and is reflected inwhole or part at an angle that is captured by an image sensor, camera,or observed by a viewer. An example of a specular reflection is theredirection of light that occurs on the surface of a smooth metal. Aspecular reflection can appear to be diffuse, for example, when it isredirected from the surface of matte metal finish. To differentiate thisphenomenon, such specular reflections that appear diffuse are referredto herein as “diffuse specular reflections.” “Glare” means specularreflection or diffuse specular reflection or any combination of specularreflection, diffuse specular reflection and diffuse reflection of anarea where the resulting reflection is detectably greater than thediffuse reflection of a surrounding area. “Glare artifact” means theportion or area or region of an object or an image of an object thatappears to emanate or emanates glare.

II. Components of the Imaging Device

The overall physical construction of the imaging device as depicted inFIG. 3 and including the illumination source 40, image sensor 50,microprocessor 60 and display 70, will now be described in detail.

The illumination source 40 preferably is adapted to generate glare whenit illuminates an object. More preferably, the illumination source 40 isadapted to both provide sufficient illumination to measure an object andgenerate glare from the object. In the most preferred embodiment, thesource 40 is a directional illumination source that produces asubstantially collimated beam of light. Optionally, two illuminationsources (not shown) may be used, where one generates glare and the otherilluminates the object for measurement. Additional sources may be addedto perform either function. Examples of other glare-generatingillumination sources that may be include, for example, a light-emittingdiode or an illumination source that projects a focused or semi-focusedbeam of light. Illumination source 40 preferably provides light withinthe visible spectrum; however, it may provide light at some wavelengththat is not visible in the region of interest 28 or the displayed image23, as desired. For example, the illumination provided may be ofnear-infrared, infrared or ultraviolet bandwidths.

Optionally, the illumination source 40 is switched-off duringacquisition of an image or measurement of the sample 22 (describedbelow). This is acceptable where a secondary illumination source (notshown) is used to illuminate the sample 22 or region of interest 28 onthe sample. Turning-off the directional illumination source 40 duringimage or measurement capture reduces or eliminates glare artifacts 25and 27 from the image 23 of the sample.

In the embodiment shown in FIG. 3, the illumination source 40 is at a0/45° geometry relative to the image sensor. Specifically, theillumination axis 41 of the illumination source 40 is at a 45° anglerelative to the optical axis 52 of the imaging sensor 50. In an idealmeasuring environment of region 28, the optical axis 52 is normal tosubstantially all points in the region of interest 28. Optionally, avariety of other geometries may be used, for example, a 45°/0 geometry,a 25°/0 geometry, a 0/25° geometry, or any other geometry conducive tomeasuring reflectance characteristics.

The image sensor 50 of the imaging device includes an observation axis52, also referred to as an optical axis, which is normal to the surfaceof the sensor. In most measuring situations, it is desirable to orientthis optical axis at a particular angle relative to the region ofinterest. Such orientation is referred to as the “angular orientation”of the image sensor and/or imaging device. In many cases, it isdesirable that the angular orientation of the imaging device is suchthat the optical axis of the image sensor is substantially normal to theregion of interest; however, depending on the surface or characteristicsto be measured, other angles may be selected.

The image sensor preferably is a charge coupling device (CCD) capable ofdetecting color. Other image sensors, such as monochromaticcomplimentary metal-oxide semiconductors (CMOS) may be substituted forthe CCD as desired. Optics may be employed as necessary to form an imageof the sample on the image sensor. Further, spectrally selective opticalelements may be added to the device 20 as desired, for example bandpassfilters and the like. Moreover, the spectral bandpass function measuredby the image sensor may be modified or additional components added toobtain a desirable measurement. As a general example, the image sensormay be spectrally selective, that is, it may act as a spectrophotometer,a colorimeter, or a densitometer when modified or combined with othercomponents. As a more specific example, the image sensor may be amonochrome image sensor used in conjunction with tailored illuminationand broadband filters in an imaging colorimeter to provide a desiredmeasurement. Optionally, the image sensor may be replaced with aconventional photographic camera.

The image sensor is in communication with the display 70 so thatinformation may be transferred from the image sensor to the display 70for output of an image 23 on the display. Preferably, the display is aliquid crystal display capable of displaying the captured image incolor; however, a monochromatic display may also be used. The image 23of the sample 22 is preferably a live video feed to the display 70,however, the image 23 may be a still video image in some applications.

The display may further include an information field 77 that providestext or graphical instructions to a user. As shown in FIG. 4, thedisplay includes arrows 78 (in an inactivated state), which indicate thedirection that the imaging device 20 must be adjusted to obtain adesired angular orientation relative to the sample 22. Optionally, theinformation field 77 may be disposed around the perimeter of the display70 with the arrows 78 disposed on each of the sides of the displayperimeter 77, or any other configuration that facilitates understandingof information conveyed by the display.

The display also is adapted to generate highlighting areas 30 and 32 inan image of the sample 23 which corresponds to the glare artifacts ascaptured by the image sensor. The highlighted areas 30 and 32 mayalternatively or additionally correspond to the ideal positions of theglare artifacts within the image to obtain a desired angular orientationof the device 20. The number, shape, orientation and highlighting mayvary depending on the image captured or the desired settings of theuser. For example, as shown, the highlighted areas 30 and 32 aredepicted as broken lines. Optionally, the highlighted areas may beindicated in full lines outlining the glare artifacts 25 and 27.Alternatively, the highlighted areas 30 and 32 may be shaded or coloredcompletely within the boundaries thereof and coincident with theartifacts 25 and 27.

The imaging device 20 further includes a processor 60 in communicationwith the image sensor 50 and display 70. Optionally, where a smaller,portable imaging device is needed, or where large processors arerequired to make complex computations, the processor may be external tothe imaging device. In such situations, communication between theprocessor and other components of the imaging device may be establishedvia direct electrical or conventional remote communication systems.

The processor of the current embodiment includes sufficient memory tostore predefined, or “preferred,” or “ideal” locations of glareartifacts within an image of a sample to attain desired angularorientation of the imaging device. The processor further includessufficient processing capabilities to generate on the display 70instructions to adjust the angular orientation of the imaging device 20and align glare artifacts 25 and 27 with locations 30 and 32. Thisprovision of instructions is generally referred to as “steering” theuser. As will be appreciated, in embodiments where the imaging device 20is held by a fixture or machine, for example, a robot, the processor canprovide sufficient instructions to the robot to reorient the imagingdevice and establish the desired angular orientation.

Further, the processor includes sufficient memory to store multiplecaptured images of samples and the information associated with thoseimages. The processor optionally may include a communication means fordownloading images stored in the memory of the processor or allowingsimultaneous viewing of the image on the display 70 on another display(not shown). Suitable communication means include, but are not limitedto: USB connections; wireless connections; high-data transfer speedconnections (e.g., connections available under the common name,“Fire-Wire”); and connections available under the common name“Ethernet.” The processor should further include sufficient processingcapabilities to carry out the operations of the imaging device in use asexplained in detail below.

III. Operation and Method of Use

The present invention enables a user to attain a desired angularorientation of an imaging device 20 relative to a region of interest ona sample to properly measure reflectance characteristics associated withthat region.

With reference to FIGS. 5-7 there will now be described a preferredprocess of the present invention. As a first step in the process, a userdisposes the imaging device 20 adjacent a region of interest 28 on thesample 22 that the user wants to measure. The user generally attempts toensure that the sample 22 is within the field of view of the imagesensor 50, so that an image 123 of the sample is displayed on thedisplay 70. As will be appreciated, the image 123 is displayed in theperspective in which the image sensor sees the sample. As the image 123is displayed, the illumination source 40 is activated eitherautomatically by the device or manually by the user, to impinge incidentrays 280-282 onto the surfaces of the sample 22. As shown in FIG. 5,this results in rays 281 and 282 being reflected directly off thesurface of the sample in areas 224, 226, as reflected rays 284 and 285,which are directed back along the optical axis 52 of the image sensor.Accordingly, these regions 224 and 226 are represented as glareartifacts 125 and 127 in the resulting image 123. Optionally, the glareartifacts 125 and 127 may be highlighted as desired if they are notwell-defined on the display. For example, the measured glare artifactsmay be outlined or colored differently on the display 70. If the sample22 is brightly colored, the contrast difference of the glare artifacts125 and 127 may be enhanced, or alternatively, the lightness or color ofthose artifacts 125 and 127 may be changed to an artificial value tofurther call out the artifacts for the user.

As the image of the sample 123 is displayed with measured glareartifacts 125 and 127 associated with it, the processor analyzes theposition of those glare artifacts. Specifically, the processor definesthe boundaries or perimeter of the sample in the image using techniquesknown in the art. The processor generates relationships between theperimeter and the location of the measured glare artifacts 125 and 127in the image to identify where, in the area bound by the image sample123, the artifacts are located. With the location of the measuredartifacts 125 and 127 defined, the processor compares those locations topreferred locations of the artifacts 30 and 32, which are highlighted onthe display as shown, but need not be highlighted in actual use. Thesepreferred locations of the artifacts also referred to as predeterminedlocations or ideal locations and may be determined in a variety of waysas explained in further detail below.

Based on the comparison, the processor generates a steering functionthat represents the adjustment of the angular orientation of the imagingdevice (i.e., adjustment of the optical axis 52 of the image sensorrelative to region 28) necessary to move the measured glare artifacts125 and 127 so that they register or coincide with the preferredlocations 30 and 32. As shown in FIG. 6, the steering function may beoutput in the information field as highlighted arrow 78 with optionaltext 79 to instruct the user to adjust the imaging device in thedirection indicated. Assuming the user desires to obtain a measurementof the region of interest 28 with the imaging device in an ideal angularorientation, the user subsequently adjusts the angular orientation ofthe imaging device 20 relative to the sample in the direction of thearrow 130. As will be appreciated, if a mechanical apparatus, such as arobot, is used to position the imaging device, the processor mayinstruct the robot to carry out the steering function and adjust theangular orientation of the imaging device.

It will be appreciated that steering need not be implemented if a userknows the position of the preferred glare artifact location. In such asituation, the user intuitively adjusts the device until the measuredglare artifacts 124 and 126 are positioned in the user-known, predefinedlocations.

In the current embodiment where steering is used, throughout theadjustment of the angular orientation of the imaging device 20, theimage of the sample 22 on the display 70 is updated. The user may watchas the glare artifacts 125 and 127 change in relation to the surface ofthe displayed sample 123. Ideally, the user stops adjusting the imagingdevice when the display no longer outputs adjustment arrows 78, or whenthe measured glare artifacts 25 and 27 coincide with preferred glareartifact locations 30 and 32 as shown in FIG. 7.

FIG. 7 depicts the imaging device immediately after the angularorientation of the instrument 20 is adjusted by the user to achieve anangular orientation wherein the optical axis 52 of the image sensor isnormal to the region of interest 28. This orientation may be confirmedby observing the measured glare artifacts 25 and 27 displayed in theimage 23 in registration with the preferred glare artifact locations 30and 32.

At this point, the user captures the image of the sample 23. Optionally,the preferred glare artifact locations 30 and 32 may be highlightedduring image capture on the display to assist the user in steadying theinstrument. Moreover, the information field 77 of the display 70 maydisplay text 79 to instruct the user to acquire the image.

With reference to FIGS. 8 and 8A, there will now be described apreferred technique to study the ideal locations of glare artifacts inan image and establish an adjustment protocol to attain a desiredangular orientation for a specific object or class of objects. Thisexample uses an experimental process for determining the ideal locationsof glare artifacts. Although the example is disclosed in relation to themeasurement of color and translucence of teeth to create dentalrestorations, it will be appreciated that it is also applicable tovirtually any application requiring measurement of an object withaccuracy or consistency.

The shape of the teeth can vary greatly, however, most teeth have convexcurved surfaces with a decreasing radius of curvature close to the gumline which corresponds to the cervical edge of the tooth. Teeth tend tohave the flattest surfaces in a central region of the tooth. Moreover,the central region of the tooth generally represents the overall colorof the tooth, and if restorations are constructed to match this centralregion, then the restoration generally matches the natural tooth. Thus,it is desirable to obtain proper measurements of the central region ofthe tooth.

With reference to FIG. 8, this is accomplished by assuring that theoptical axis 52 of the image sensor 50 is normal to that region duringmeasurement. With imaging device 20 mounted in the fixture 90, the ideallocation of glare artifacts within images of shade guides, and teeth ingeneral, was established to ensure consistent angular orientation of theimaging device relative to teeth during measurements. The imaging device20 shown in FIG. 8 includes the same components as the imaging devicedescribed above, however, the measuring geometry of the imaging sensorrelative to the illumination source is 0/18°. This means that theoptical axis during measurement is normal to the measured region ofinterest and the axis of illumination 41 is disposed at an angle D whichis 18° from the optical axis 52. The imaging device 20 may optionally beoutfitted with an optional spacing device (not shown) that spaces theshade guide 92 a pre-specified distance from the image sensor to ensureconsistent lighting of the shade guide 92. 21 The imaging device 20 ismounted in fixed relation to the fixture 90 with mounting bracket 91. Ashade guide tab 92 likewise is mounted to the fixture with a mount 93 infixed relation to the fixture 90. A carpenter square 94, or otherpractical means is further associated with the fixture 90 to establish anormal relation between the points of the shade guide corresponding tothe central location of the tooth 102 (FIG. 8A) and the optical axis 52of the image sensor. In an experimental measuring sequence, the positionof the glare artifact created by incident light 128, reflecting offshade guide tab 92 as reflected ray 129, was analyzed to determine theideal location of glare artifacts in an image of a tooth. It was foundthat to ensure the optical axis 52 is normal to the central region 102of the tooth, the glare artifact should be positioned in area 104, asshown in FIG. 8A, which is a display of the imaged shade guide 96 ondisplay 70. Specifically, when the glare artifact is positioned on ashade guide, or tooth, in region 104, a user can be reasonably certainthat the optical axis 52 of the image sensor 50 is normal to the centralregion of the tooth 102, which is region of interest in mostapplications. Region 104 is centered on a point about one-third of thedistance 100 from the cervical edge 98 of the tooth to the incisal edge99 of a tooth.

Testing may be conducted to confirm that the experimentally determined,ideal locations of glare artifacts are able to assist in angularorientation during an actual measuring scenario. Regarding the aboveexperimentally determined ideal glare artifact locations for dentalmeasurements, several tests were conducted to this effect. In one test,untrained operators used the imaging device to measure color andappearance variables of human teeth. To do so, they were told toactivate the imaging device and illuminate the tooth. They wereinstructed to view the display and manipulate the imaging device so thatglare artifacts created by the illumination was centered on a pointabout one-third the distance from the cervical edge of the tooth to theincisal edge of the tooth. The operators then captured measurement ofthe tooth. Upon analysis of the measurement data, it was determined thatsuch positioning of the glare artifacts within an image of the toothcaused the instrument to function correctly. Specifically, the datasuggested that the optical axis of the image sensor of the imagingdevice was normal to the central region of the tooth during measurement.

In other testing of the experimentally determined ideal glare artifactlocations for dental measurements, an operator trained in proper angularorientation measured a tooth without regard to the position of the glareartifact in the image. Upon analysis of the measurement taken at theangular orientation specified by the trained observer, it was confirmedthat the ideal glare artifact location was in a region about one-thirdthe distance from the cervical edge of the tooth to the incisal edge ofthe tooth.

Thus, with the confirmatory testing methods above, ideal glare artifactlocations may be confirmed so that users may reliably establish anangular orientation of an imaging device relative to an object to obtainuseful measurement of that object. In the case of dental measurementimaging devices, this is particularly helpful because the angularorientation may be established in a freehanded manner that otherwisewould require the use of a fixture.

An alternative to the experimental technique described above usescommercially available three-dimensional computer aided drafting(3D-CAD) or photo-rendering software to determine the location of glareartifacts that are characteristic of an ideal angular orientation of animaging device relative to an object. In the first step of such aprocess, the angular orientation of a real imaging device to a realobject is determined. For example, an ideal angular orientation of areal imaging device to a real object may be such that the optical axisof an image sensor of the real imaging device is normal to a specificsurface of the real object.

Using a commercially available 3D-CAD for photo-rendering softwarepackage, for example, Pro/ENGINEER available from ParametricTechnologies Corporation of Needham, Mass., a three-dimensional model ofthe real object is created or imported. Within the 3D-CAD orphoto-rendering software package, the modeled object is oriented tomimic the view direction of the real imaging device in the ideal angularrelation determined above. For example, the modeled object is orientedto replicate the real object as if it were imaged by the real imagingdevice in the ideal angular orientation.

In another step, the 3D-CAD or photo-rendering software package is usedto create a directional lighting specification that matches orapproximately matches the directional lighting expected when the realimaging device measures the real object. In yet another step, the 3D-CADor photo-rendering software package renders or artificially shades themodeled object in accordance with the created directional lightingspecification and the determined ideal angular orientation specified inthe first step. The image rendered will show the preferred glareartifact locations within the rendered image that are characteristic ofthe ideal angular orientation as viewed by the real imaging deviceduring actual measurement.

As will be appreciated, other techniques may be used to determine thepreferred locations of glare artifacts characteristic of ideal angularorientations of the imaging device and the measured object relative toone another.

IV. First Alternative Embodiment

An alternative embodiment 300 of the present invention is illustrated inFIG. 9. The imaging device 300 includes an image sensor 350 having anoptical axis 352, a directional illumination source 340 and a processor360 as described above. The imaging device 300 is mounted in relation toa conveyor system 330 that moves product 322 past the imaging device 300in a time varying manner. This set-up may be used in an inspectionstation on a production line to ensure consistency of product, forexample, homogeneous and consistent color.

As shown, the sample 322 is a computer mouse that is moved relative tothe optical axis 352 and illumination axis 341 of the imaging device 300through positions 312, 314, 316 and 318. The sample 322 has a region ofinterest 328 for which measurement of reflectance characteristics isdesired.

In this embodiment, as the conveyor 330 conveys the sample 322 past theimaging device 300, the imaging device monitors the position of theglare artifact generated by light reflected from the surface of thesample 322. More specifically, as the sample 322 traverses positions312, 314, 316 and 318, the image sensor detects the position of sample322 in the image sensor's field of view. The sensor 350 further sensesthe relative position of the glare artifact created by light rays fromillumination source 340 reflecting off the surface of the sample 322.The field of views of the image sensor as the sample moves are shown inscenes 312, 314, 316 and 318. The processor 360 monitors therelationship between the glare artifacts 313, 315, 317 and 319 and thepreferred glare artifact location 330. The preferred glare artifactlocation 330 corresponds to an ideal position of the sample 322 relativeto the optical axis 352 for capturing a useable image of the region ofinterest 328. Only when an acceptable orientation of the glare artifact,specifically, when the glare artifact 317 substantially registers withpreferred location 330, does the image sensor capture an image of thesample 322. Scene 316 depicts that acceptable orientation and isoutlined to indicate that the image is acquired when the glare artifact317 is in registration with the predefined location 330. In thisconfiguration, also shown in solid lines in the side view of the imagingdevice 300, the image sensor is substantially normal to a statisticallyrelevant number of points in the region of interest 328. In all of theremaining scenes 312, 314 and 318, the glare artifacts 313, 315 and 319are not in registration with the preferred location 330. Accordingly,the image sensor does not record an image when the sample 322 is inthese orientations because the ideal angular orientation of the imagesensor is not present. After an image is acquired, the measurement datamay then be derived from the region of interest 328 of that image.

As will be appreciated, the above first alternative embodiment may bemodified so that the imaging device moves relative to a stationarysample. This modified system also would operate under the principles ofthe above process.

V. Second Alternative Embodiment

The second alternative embodiment of the invention is also explainedwith reference to FIG. 9. The imaging device 300 operates under the sameprinciples as described in reference to the first alternative embodimentabove; however, instead of waiting to acquire an image when theprocessor 360 detects registration of a measured glare artifact 317,e.g., the orientation shown in scene 316, the microprocessor stores andrecords images for multiple scenes, here, each different scene 312, 314,316 and 318. These recorded images are reviewed by the processor or anoperator to select the image having the best glare positioning, i.e.,image 316 having glare artifact 317 in registration with preferredlocation of the glare artifact 330. Measurement data may then be derivedfrom the region of interest 328 of the selected image and the otherimages discarded.

As in the second alternative embodiment above, the process of thisembodiment may be effectively used where the imaging device 300 movesrelative to a fixed sample 322.

VI. Third Alternative Embodiment

A third alternative embodiment 400 of the invention is illustrated inFIG. 10. Imaging device 400 is generally identical to the physicalconstruction of imaging device 300 with the exception that multiple,directional illumination sources 440, 442, 444 and 446 are included inthe device. Moreover, the sample 422 is of a different shape from sample322. With the additional illumination sources, many more glare artifactsare created and detected by the image sensor 450. These multiple glareartifacts may be used to more positively confirm that the optical axis452 is normal to a desired region of interest on the surface of thesample.

As shown, the glare created by the multiple illumination sources isdetected by the image sensor 450 and output as multiple glare artifacts480 , 482, 484 and 486 on the display 470. By ensuring that these glareartifacts register with predefined glare artifact locations 490, 492,494 and 496, respectively, a user or the system may positively confirmthat the ideal angular orientation is established between the imagesensor 450 and a region of interest on the surface of the sample 422.

Given multiple illumination sources, it may be difficult to associateone illumination source with a particular glare artifact. Severaloptions are available to solve this problem. For example, eachillumination source 440, 442, 444 and 446 may be appropriately modulatedin intensity differentiate each in time. As another example, each source440, 442, 444 and 446 may be of a different color or spectralcomposition. Both examples provide a way to reduce confusion among glareartifacts. These and other techniques-may also be applied to the otherembodiments herein as desired.

VII. Fourth Alternative Embodiment

A fourth alternative embodiment 500 of the invention is shown in FIG.11. The imaging device 500 is generally identical to the imaging device400, with the exception that instead of having multiple illuminationsources, imaging device 500 includes one illumination source 541 that ismoved to multiple positions 540, 542, 544 and 546 to vary its angularrelationship relative to the image sensor 550 and sample 522 over time.Consequently, a larger number of glare artifacts may be measured andcompared to predefined glare artifact locations to ensure accurateangular orientation of the imaging device 500 relative to the sample522.

The output of glare detected by the image sensor 550 on the display 570is also similar to that of the display 470 of the third alternativeembodiment, except that a different image is generated for eachdifferent location 540, 542, 544 and 546 of the illumination source 541.As with the third alternative embodiment, by ensuring the glareartifacts 580, 582, 584 and 586 substantially register with predefinedlocations 590, 592, 594 and 596, respectively in each respective image,a user can confirm the ideal angular orientation is established betweenthe image sensor 550 and a region of interest to the surface of thesample 522.

The illumination source need not move in a circular, time-varying path,but may optionally move in any time-varying angular relationshiprelative to the image sensor 550, the sample 522, or both, that isconducive to generating multiple glare artifacts in an image of asample. Moreover, additional time-varying illumination sources may beadded as desired.

The present invention provides a system and method for acquiring adesired angular orientation of an imaging device relative to a sample toensure that measurements of the sample are accurately and consistentlycaptured. The real-time steering and visual confirmation of idealadjustment, using the relative positioning of glare artifacts within animage, eliminates the guess-work associated with orienting an imagingdevice for a measurement. Although the imaging device of the presentinvention has been disclosed in connection with dental and manufacturingapplications, the invention is applicable to virtually any reflectancecharacteristic measurement instrument using any reflectancecharacteristic measurement technology. Further, although the inventionhas been described in connection with generally glossy materials, whichgenerate specular reflections, the invention is applicable tomeasurement of matte-finish objects which generate diffuse specularreflections and hybrids of matte-finish objects and glossy objects.

The above descriptions are those of the preferred embodiments of theinvention. Various alterations and changes can be made without departingfrom the spirit and broader aspects of the invention as defined in theappended claims, which are to be interpreted in accordance with theprinciples of patent law including the Doctrine of Equivalents. Anyreferences to claim elements in the singular, for example, using thearticles “a,” “an,” “the,” or “said,” is not to be construed as limitingthe element to the singular.

1. A method for adjusting an imaging device that includes an imagesensor relative to an object comprising: locating the image sensor ofthe imaging device relative to the object; illuminating the object tocreate glare; detecting the glare with the image sensor; and adjusting aposition of the image sensor relative to the object based on arelationship between a present position of the detected glare relativeto the object and a desired position of the glare relative to theobject.
 2. The method of claim 1 comprising displaying the glare to auser on a display.
 3. The method of claim 2 wherein the imaging deviceinstructs the user to perform said adjusting.
 4. The method of claim 3wherein the display displays arrows to direct a user in said adjusting.5. The method of claim 2 comprising highlighting the glare on thedisplay.
 6. The method of claim 1 wherein said illuminating is performedwith a source at a position distanced from the object and the imagesensor, and wherein the position is time-varied relative to at least oneof the image sensor and the object.
 7. The method of claim 1 wherein theobject is at least one of a human tooth and a shade guide tab, includinga cervical edge and an incisal edge, the cervical edge disposed adistance from the incisal edge.
 8. The method of claim 7 wherein theposition of the image sensor is adjusted relative to the at least one ofa human tooth and a shade guide tab to ensure that the glare is locatedat a predefined position relative to the at least one of a human toothand a shade guide tab.
 9. The method of claim 1 comprising repeatingsaid aforementioned steps to identify a desired location of the glare inan image, the desired location corresponding to an optimal angularorientation of the imaging device relative to the object.
 10. A methodfor steering an imaging device disposed in a first orientation relativeto an object, the object illuminated such that a glare artifact isvisible in a first location on the object, comprising: sensing the glareartifact; and providing instructions to move the glare artifact to asecond location on the object based on said sensing, whereby the imagingdevice is adjusted to a second orientation relative to the object. 11.The method of claim 10 wherein the instructions are provided to a user.12. The method of claim 11 where the imaging device includes a displayand the instructions are provided to the user via an arrow on thedisplay.
 13. The method of claim 10 wherein the detected glare artifactis displayed in an image including at least a portion of the object. 14.The method of claim 13 comprising highlighting the glare artifact in thefirst location.
 15. The method of claim 14 comprising indicating whenthe glare artifact is in the second location.
 16. The method of claim 10wherein the object includes a non-planar surface.
 17. The method ofclaim 16 wherein the second location substantially corresponds toone-third of the distance away from the cervical edge of the tooth. 18.The method of claim 10 wherein the object is at least one of a humantooth and a shade guide tab including a cervical edge, an incisal edge,and a region representative of the reflectance characteristics of the atleast one of a human tooth and a shade guide tab, the cervical edgedisposed a distance from the incisal edge, and wherein the imagingdevice includes an image sensor having an optical axis.
 19. The methodof claim 18 wherein the second orientation provides alignment of theoptical axis so that the optical axis is substantially normal to theregion.
 20. A method for attaining a desired angular orientation of animaging device relative to an object, the method comprising: sensing theobject and a glare artifact associated with the object; determining aposition of the glare artifact relative to the object; and determiningthe desired angular orientation based on the determined position of theglare artifact.
 21. The method of claim 20, wherein said determining aposition of the glare artifact includes defining a boundary of an imageof the object.
 22. The method of claim 20, wherein said determining thedesired angular orientation includes comparing the determined positionof the glare artifact to a preferred position of the glare artifact. 23.The method of claim 20, further comprising illuminating the object. 24.The method of claim 20, further comprising displaying an image of theobject.
 25. The method of claim 24, wherein said displaying the imageincludes highlighting an area associated with the glare artifact. 26.The method of claim 20, further comprising generating an instruction toadjust the angular orientation of the imaging device.
 27. The method ofclaim 20, further comprising adjusting the angular orientation of theimaging device.
 28. The method of claim 27, wherein said adjusting theangular orientation of the imaging device includes aligning an opticalaxis of an image sensor of the imaging device substantially normal to asurface of the object.
 29. The method of claim 20, further comprisingmeasuring a characteristic of the object.